Southern Kings face the possibility of being expelled in their first Super Rugby season after the South African Rugby Union (SARU) launched an investigation of the newcomers for fielding too many foreign players.

SARU said on Tuesday it was looking into "a suspected breach" of its Super Rugby contract with the Port Elizabeth-based Kings, which stipulates South African teams cannot field more than two foreign players in a game.

The Kings picked New Zealander Hadleigh Parkes at centre in the 35-24 home loss to the defending champions Chiefs on Friday, while Argentine players Tomas Leonardi and Nicolas Vergallo were used off the bench.

"Jurie Roux, CEO of SARU, contacted Cheeky Watson, the chairman of the Kings board, on Tuesday to advise him of the inquiry and also to caution him against any potential breaches," SARU said in its statement, which came after days of speculation in South Africa surrounding the Kings' alleged wrongdoing.

SARU held an emergency meeting via a telephone conference on Tuesday and appointed a judicial committee to investigate the Kings.

The definition of a foreign player in South African rugby was unclear and still "up for a lot of debate", Kings president and chairman Watson said this week before the investigation was announced. Players from Africa, like the Kings' Daniel Adongo, a Kenyan, are not considered foreign players in South Africa.

The two-player limit is a South African rule for its own teams and not enforced by Super Rugby organiser SANZAR across the three-country tournament. The Kings asked SARU to relax its limit on foreign players to help them in their first season, but the national union refused and maintained the two-player limit in a public statement.

The Kings squad is in New Zealand to play the Crusaders in Christchurch this Saturday, and then the Hurricanes in Wellington the weekend after, before moving to Australia to face ACT Brumbies and Melbourne Rebels.

Parkes, Leonardi, Vergallo and another foreign player, Frenchman Virgile Lacombe, were in the Kings' travelling squad for the four-game tour of New Zealand and Australia.

The Kings later responded by saying they had been led to believe Argentine players would not be classified as foreign because of the presence of a team from Argentina in one of South Africa's domestic competitions.

"In the process leading up to the signing of foreign players last year," Watson said, "we were led to believe and even encouraged to sign Argentinean players ... with the understanding that they would not be considered as foreign players."

Still, Watson said the Kings would now "submit to the guidance of the governing body of SARU".